From the viewpoint of space saving, in recent years, there have been widely used, in place of a CRT type display conventionally used, flat panel displays such as a liquid crystal display, a plasma display, an OLED display, and a field emission display. Further reduction in thickness is demanded for those flat panel displays. In particular, it is required that the OLED display be easily carried by being folded or rolled and be usable not only on a flat surface but also on a curved surface. Further, it is not just displays that are required to be usable not only on a flat surface but also on a curved surface. For example, if a solar cell or an OLED lighting device can be formed on a surface of an object having a curved surface, such as a surface of an automobile body, or a roof, a pillar, or an outer wall of a building, the applications of the solar cell or OLED lighting device may expand. Substrates and cover glasses to be used for those devices are therefore required to be a thinner sheet and to have high flexibility.
A light-emitting member to be used for an OLED display deteriorates in quality through the contact of gasses such as oxygen and water vapor. Thus, a substrate to be used for the OLED display is required to have high gas-barrier property, and hence the use of a glass substrate for the substrate is expected. However, glass to be used for a substrate is weak in tensile stress unlike a resin film, and hence is low in flexibility. Thus, when a glass substrate is made bend and thereby being generated a tensile stress on a surface of the glass substrate, the glass substrate tends to be damaged. In order to impart flexibility to the glass substrate, the glass substrate is required to achieve an ultra thin sheet. Thus, a glass film having a thickness of 200 μm or less is proposed as disclosed in Patent Literature 1 below.
A glass substrate to be used for electronic devices such as a flat panel display and a solar cell is subjected to various kinds of processing associated with electronic device manufacture, such as processing for providing a film such as a transparent conductive film and cleaning processing. However, when a glass film is used as a glass substrate for those electronic devices, the glass film is damaged due to a stress change even at a small amount, because glass is a brittle material. Thus, there is a problem in that the handling of the glass film is very difficult, when the above-mentioned various kinds of processing associated with electronic device manufacture are carried out. In addition, there is another problem in that a glass film having a thickness of 200 μm or less is rich in flexibility, and hence the positioning of the glass film is difficult when the processing associated with manufacture is carried out.
Therefore, in order to improve a handling property of the glass film, there is proposed a laminate disclosed in Patent Literature 2 below. Patent Literature 2 below proposes a laminate in which a supporting glass substrate and a glass sheet are laminated through intermediation of a pressure-sensitive adhesive layer that may be maintained almost stably even after its repeated use. According to this kind of laminate, even when a glass sheet itself having less strength and rigidity is used, a liquid crystal display device can be manufactured while sharing a conventional liquid crystal display device manufacturing line. Also, after completion of the manufacturing steps, the glass substrate can be peeled off. Further, because the supporting member is used, the positioning can be easily performed when the processing associated with manufacture is carried out.
However, when the glass sheet is further ultra thinned to become a glass film, even in the above-mentioned laminate, it is difficult to peel off the glass film from the supporting glass substrate after the electronic device is manufactured. When the glass film is to be peeled from the supporting glass substrate, the peeling is started from a corner portion of the glass film. However, in the laminate described in Patent Literature 2, the entire surface of the glass film is brought into contact with the supporting glass substrate. Therefore, there is a problem in that, because the corner portion of the glass film is difficult to grasp, breaking or chipping are liable to occur at the corner portion of the glass film during peeling of the glass film. In particular, when a strong adhesive force is present between the glass film and the supporting glass, this problem becomes conspicuous. In order to solve this problem, the glass film may be laminated on the supporting glass substrate so that a part of the glass film protrudes from the supporting glass substrate. However, in this case, there is a problem in that, when a pin or the like strikes the laminate at the time of positioning, the part of the glass film protruding from the supporting glass substrate may be broken.
In order to solve the above-mentioned problem, Patent Literature 3 below disclosed a glass laminate constituted by a thin glass substrate and a supporting glass substrate which is provided with recessed portions at an end portion thereof. An end portion of the thin glass substrate exposed at the recessed portions can be grasped, and therefore the thin glass substrate can be prevented from breaking when peeling. Further, the supporting glass substrate is a size larger than the thin glass substrate, and hence the breaking of the thin glass substrate due to the striking of the pin or the like at the time of positioning can also be prevented to some extent.